-
G. Laveissière,
N. Degrande,
S. Jaminion,
C. Jutier,
L. Todor,
R. Di Salvo,
L. Van Hoorebeke,
L. C. Alexa,
B. D. Anderson,
K. A. Aniol, [......],
E. Voutier,
J. W. Watson,
L. B. Weinstein,
K. Wijesooriya,
R. Wilson,
B. B. Wojtsekhowski,
D. G. Zainea,
W-M. Zhang,
J. Zhao,
Z.-L. Zhou
[show abstract]
[hide abstract]
ABSTRACT: Exclusive electroproduction of π0 mesons on protons in the backward hemisphere has been studied at Q2=1.0 GeV2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab’s Hall A. The data span the range of the total (γ*p) center-of-mass energy W from the pion production threshold to W=2.0 GeV. The differential cross sections σT+ϵσL, σTL, and σTT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.
Phys. Rev. C. 04/2004; 69(4).
-
K A Aniol,
D S Armstrong,
T Averett,
M Baylac,
E Burtin,
J Calarco,
G D Cates,
C Cavata,
Z Chai,
C C Chang, [......],
J Mcintyre,
D Relyea,
Y Roblin,
J Roche,
G A Rutledge,
P M Rutt,
M Rvachev,
F Sabatie,
A Saha,
P A Souder
N. Liyanage J. Mitchell T. Pussieux R. D. Ransome R. Suleiman J. Templon T. Teresawa J. Thompson R. Tieulent P. E. Ulmer. 03/2004; 331218123327819(19).
-
X Zheng,
K Aniol,
D S Armstrong,
T D Averett,
W Bertozzi,
S Binet,
E Burtin,
E Busato,
C Butuceanu,
J Calarco, [......],
G Urciuoli,
A Vacheret,
B Wojtsekhowski,
H Xiang,
Y Xiao,
F Xiong,
B Zhang,
L Zhu,
X Zhu,
P A Zołnierczuk
[show abstract]
[hide abstract]
ABSTRACT: We have measured the neutron spin asymmetry A(n)(1) with high precision at three kinematics in the deep inelastic region at x=0.33, 0.47, and 0.60, and Q(2)=2.7, 3.5, and 4.8 (GeV/c)(2), respectively. Our results unambiguously show, for the first time, that A(n)(1) crosses zero around x=0.47 and becomes significantly positive at x=0.60. Combined with the world proton data, polarized quark distributions were extracted. Our results, in general, agree with relativistic constituent quark models and with perturbative quantum chromodynamics (PQCD) analyses based on the earlier data. However they deviate from PQCD predictions based on hadron helicity conservation.
Physical Review Letters 02/2004; 92(1):012004. · 7.37 Impact Factor
-
T. Reichelt,
R. Madey,
A.Yu. Semenov,
S. Taylor,
A. Aghalarian,
E. Crouse,
G. MacLachlan,
B. Plaster, S. Tajima,
W. Tireman, [......],
S. Wells,
F. Wesselmann,
S. Wood,
C. Yan,
S. Yang,
L. Yuan,
W.M. Zhang,
H. Zhu,
X. Zhu,
H. Arenhovel
[show abstract]
[hide abstract]
ABSTRACT: The ratio G{sub c}{sup n}/G{sub m}{sup n} of the electric to the magnetic form factor of the neutron has been measured by analyzing the polarization of the recoiling neutron in quasi-elastic scattering of longitudinally polarized electrons from deuterium at the Q{sup 2} values of 0.45, 1.15, and 1.47 (GeV/c){sup 2}. The experiment has been performed in Hall C of the Thomas Jefferson National Accelerator Facility. With G{sub m}{sup n} being known G can be deduced. The preliminary results show that the lowest Q{sup 2} points follow the Galster parameterization and that the 1.47 (GeV/c){sup 2} point rises above this parameterization.
10/2003
-
R Madey,
A Yu Semenov,
S Taylor,
B Plaster,
A Aghalaryan,
E Crouse,
G MacLachlan, S Tajima,
W Tireman,
Chenyu Yan, [......],
J W Watson,
S Wells,
F Wesselmann,
S Wood,
Chen Yan,
S Yang,
L Yuan,
W-M Zhang,
H Zhu,
X Zhu
[show abstract]
[hide abstract]
ABSTRACT: We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G(n)(E)/G(n)(M), obtained via recoil polarimetry from the quasielastic 2H(e-->,e(')n-->)1H reaction at Q2 values of 0.45, 1.13, and 1.45 (GeV/c)(2) with relative statistical uncertainties of 7.6% and 8.4% at the two higher Q2 points, which points have never been achieved in polarization measurements.
Physical Review Letters 09/2003; 91(12):122002. · 7.37 Impact Factor
-
S Strauch,
S Dieterich,
K A Aniol,
J R M Annand,
O K Baker,
W Bertozzi,
M Boswell,
E J Brash,
Z Chai,
J-P Chen, [......],
A Sarty,
J M Udias,
P E Ulmer,
G M Urciuoli,
J F J van den Brand,
J R Vignote,
D P Watts,
L B Weinstein,
K Wijesooriya,
B Wojtsekhowski
[show abstract]
[hide abstract]
ABSTRACT: We have measured the proton recoil polarization in the 4He(e-->,e(')p-->)4H reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of final-state interactions is under control.
Physical Review Letters 08/2003; 91(5):052301. · 7.37 Impact Factor
-
R. Madey,
A.Yu. Semenov,
S. Taylor,
A. Aghalaryan,
E. Crouse,
G. MacLachlan,
B. Plaster, S. Tajima,
W. Tireman,
Chenyu Yan, [......],
J.W. Watson,
S. Wells,
F. Wesselmann,
S. Wood,
Chen Yan,
S. Yang,
L. Yuan,
W.-M. Zhang,
H. Zhu,
X. Zhu
[show abstract]
[hide abstract]
ABSTRACT: The ratio of the electric to the magnetic form factor of the neutron,
g º GEn/GMng \equiv G_{En}/G_{Mn}
, was measured via recoil polarimetry (R.G. Arnold, C.E. Carlson, F. Gross, Phys. Rev. C 23, 363 (1981)) from the quasielastic 2H
(e®,e¢n® )(\mathop{e}\limits^{\scriptstyle\to},e' \mathop{n}\limits^{\scriptstyle\to} )
1H reaction at three values of Q2 (viz, 0.45, 1.15, and 1.47 (GeV/c)2) in Hall C of the Thomas Jefferson National Accelerator Facility. The data reveal that GEn continues to follow the Galster parameterization up to Q2 = 1.15 (GeV/c)2 and rises above the Galster parameterization at Q2 = 1.47 (GeV/c)2.
European Physical Journal A 06/2003; 17(3):323-327. · 2.19 Impact Factor
-
P E Ulmer,
K A Aniol,
H Arenhövel,
J-P Chen,
E Chudakov,
D Crovelli, J M Finn,
K G Fissum,
O Gayou,
J Gomez, [......],
R Michaels,
J Mitchell,
C F Perdrisat,
V Punjabi,
R Roché,
F Sabatie,
A Saha,
R Suleiman,
L Todor,
B B Wojtsekhowski
[show abstract]
[hide abstract]
ABSTRACT: The 2H(e,e(')p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (x(Bj)=0.964) at a four-momentum transfer squared, Q(2)=0.665 (GeV/c) (2) (omega=0.368 GeV, W=2.057 GeV), and for recoil momenta up to 550 MeV/c. The measured cross section deviates by 1-2sigma from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations.
Physical Review Letters 09/2002; 89(6):062301. · 7.37 Impact Factor
-
F Xiong,
D Dutta,
W Xu,
B Anderson,
L Auberbach,
T Averett,
W Bertozzi,
T Black,
J Calarco,
L Cardman, [......],
B Tipton,
L Todor,
M Viviani,
B Vlahovic,
J Watson,
C F Williamson,
H Witała,
B Wojtsekhowski,
J Yeh,
P Zołnierczuk
[show abstract]
[hide abstract]
ABSTRACT: We present the first precision measurement of the spin-dependent asymmetry in the threshold region of 3He(e,e') at Q2 values of 0.1 and 0.2 (GeV/c)2. The agreement between the data and nonrelativistic Faddeev calculations which include both final-state interactions and meson-exchange current effects is very good at Q2 = 0.1 (GeV/c)2, while a small discrepancy at Q2 = 0.2 (GeV/c)2 is observed.
Physical Review Letters 01/2002; 87(24):242501. · 7.37 Impact Factor
-
P E Ulmer,
K. A. Aniol,
H. Arenhoevel,
J P Chen,
E. Chudakov,
D Crovelli, J.M. Finn,
K.G. Fissum,
O Gayou,
J Gomez, [......],
R Michaels,
J Mitchell,
C. F. Perdrisat,
V. Punjabi,
R. Roche,
F Sabatie,
A Saha,
R Suleiman,
L Todor,
B. B. Wojtsekhowski
[show abstract]
[hide abstract]
ABSTRACT: The 2H(e,e'p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility (JLab) in quasielastic kinematics (x=0.96) at a four-momentum transfer squared, Q^2=0.67 (GeV/c)^2. The experiment was performed in fixed electron kinematics for recoil momenta from zero to 550 MeV/c. Though the measured cross section deviates by 1-2 sigma from a state-of-the-art calculation at low recoil momenta, it agrees at high recoil momenta where final state interactions (FSI) are predicted to be large. Comment: 4 pages, 1 figure, to be submitted to Phys. Rev. Lett
11/2001;
-
N Liyanage,
B D Anderson,
K A Aniol,
L Auerbach,
F T Baker,
J Berthot,
W Bertozzi,
P Y Bertin,
L Bimbot,
W U Boeglin, [......],
H Voskanyan,
J W Watson,
L B Weinstein,
K Wijesooriya,
R Wilson,
B Wojtsekhowski,
D G Zainea,
V Zeps,
J Zhao,
Z L Zhou
[show abstract]
[hide abstract]
ABSTRACT: We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25<E(m)<50 MeV and P(m) approximately 60 MeV/c, the reaction is dominated by a single 1s(1/2) proton knockout. At larger P(m), the single-particle aspects are increasingly masked by more complicated processes. Calculations which include pion exchange currents, isobar currents, and short-range correlations account for the shape and the transversity, but for only half of the magnitude of the measured cross section.
Physical Review Letters 06/2001; 86(25):5670-4. · 7.37 Impact Factor
-
C Mertz,
C E Vellidis,
R Alarcon,
D H Barkhuff,
A M Bernstein,
W Bertozzi,
V Burkert,
J Chen,
J R Comfort,
G Dodson, [......],
D Tieger,
C Tschalaer,
W Turchinetz,
P E Ulmer,
S Van Verst,
G A Warren,
L B Weinstein,
S Williamson,
R J Woo,
A Young
[show abstract]
[hide abstract]
ABSTRACT: High-precision 1H(e,e'p)pi(0) measurements at Q2 = 0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma*N-->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole ( I = 3/2) amplitude ratios, R(SM) = (-6.5+/-0.2(stat+sys)+/-2.5(mod))% and R(EM) = (-2.1+/-0.2(stat+sys)+/-2.0(mod))%, are dominated by model error. Previous R(SM) and R(EM) results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.
Physical Review Letters 04/2001; 86(14):2963-6. · 7.37 Impact Factor
-
W Xu,
D Dutta,
F Xiong,
B Anderson,
L Auberbach,
T Averett,
W Bertozzi,
T Black,
J Calarco,
L Cardman, [......],
B Tipton,
L Todor,
M Viviani,
B Vlahovic,
J Watson,
C F Williamson,
H Witała,
B Wojtsekhowski,
J Yeh,
P Zołnierczuk
[show abstract]
[hide abstract]
ABSTRACT: We have measured the transverse asymmetry A(T') in 3He(e,e(')) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%.
Physical Review Letters 11/2000; 85(14):2900-4. · 7.37 Impact Factor
-
S. Malov,
K. Wijesooriya,
F. T. Baker,
L. Bimbot,
E. J. Brash,
C. C. Chang, J. M. Finn,
K. G. Fissum,
J. Gao,
R. Gilman, [......],
S. van Verst,
B. Vlahovic,
H. Voskanyan,
J. W. Watson,
L. B. Weinstein,
R. Wilson,
B. Wojtsekhowski,
V. Zeps,
J. Zhao,
Z.-L. Zhou
[show abstract]
[hide abstract]
ABSTRACT: The first (e-->,e'p-->) polarization transfer measurements on a
nucleus heavier than deuterium have been carried out at Jefferson
Laboratory. Transverse and longitudinal components of the polarization
of protons ejected in the reaction 16O(e-->,e'p--> )
were measured in quasielastic perpendicular kinematics at a
Q2 of 0.8 (GeV/c)2. The data are in good agreement
with state of the art calculations.
Physical Review C 10/2000; 62(5):57302. · 3.31 Impact Factor
-
C. Mertz,
C. Vellidis,
R. Alarcon,
D. H. Barkhuff,
A. M. Bernstein,
W. Bertozzi,
V Burkert,
J Chen,
J.R. Comfort,
G. Dodson, [......],
D. Tieger,
C. Tschalaer,
W. Turchinetz,
P E Ulmer,
S. van Verst,
G. A. Warren,
L B Weinstein,
S. Williamson,
R. J. Woo,
A. Young
[show abstract]
[hide abstract]
ABSTRACT: High-precision H(e,e'p)pi0 measurements at Q2=0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma* N->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole amplitude ratios, Rsm=(-6.5 +- 0.2{stat+sys} +- 2.5{mod}) % and Rem=(-2.1 +- 0.2{stat+sys} +- 2.0{mod}) %, are dominated by model error. Previous Rsm and Rem results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account. Comment: 5 pages LATEX, 2 figures; resubmitted to Phys. Rev. Lett
02/1999;
-
J. H. Morrison,
H. Baghaei,
W. Bertozzi,
S Gilad,
J. Glickman,
C E Hyde-Wright,
N. Kalantar-Nayestanaki,
R.W. Lourie,
S. Penn,
P E Ulmer, [......],
J. Wise,
P. Boberg,
C C Chang,
D. Zhang,
K. Aniol,
M.B. Epstein,
D J Margaziotis, J.M. Finn,
C. Perdrisat,
V. Punjabi
[show abstract]
[hide abstract]
ABSTRACT: We measured the 12C(e,e'p) cross section as a function of missing energy in parallel kinematics for (q,w) = (970 MeV/c, 330 MeV) and (990 MeV/c, 475 MeV). At w=475 MeV, at the maximum of the quasielastic peak, there is a large continuum (E_m > 50 MeV) cross section extending out to the deepest missing energy measured, amounting to almost 50% of the measured cross section. The ratio of data to DWIA calculation is 0.4 for both the p- and s-shells. At w=330 MeV, well below the maximum of the quasielastic peak, the continuum cross section is much smaller and the ratio of data to DWIA calculation is 0.85 for the p-shell and 1.0 for the s-shell. We infer that one or more mechanisms that increase with $\omega$ transform some of the single-nucleon-knockout into multinucleon knockout, decreasing the valence knockout cross section and increasing the continuum cross section.
12/1998;
-
B.D. Milbrath,
J. I. McIntyre,
C. S. Armstrong,
D. H. Barkhuff,
W. Bertozzi,
D Dale,
G. Dodson,
K. A. Dow,
M.B. Epstein,
M. Farkhondeh, [......],
P.M. Rutt,
A. J. Sarty,
D. Tieger,
C. Tschalaer,
W. Turchinetz,
P E Ulmer,
S. P. Van Verst,
G. A. Warren,
L B Weinstein,
R. J. Woo
[show abstract]
[hide abstract]
ABSTRACT: Recoil proton polarization observables were measured for both the p($\vec {\rm e}$,e$^\prime\vec{\rm p}\,$) and d($\vec {\rm e}$,e$^\prime\vec{\rm p}\,)$n reactions at two values of Q$^2$ using a newly commissioned proton Focal Plane Polarimeter at the M.I.T.-Bates Linear Accelerator Center. The hydrogen and deuterium spin-dependent observables $D_{\ell\ell}$ and $D_{{\ell}t}$, the induced polarization $P_n$ and the form factor ratio $G^p_E/G^p_M$ were measured under identical kinematics. The deuterium and hydrogen results are in good agreement with each other and with the plane-wave impulse approximation (PWIA). Comment: 9 pages, 1 figure; accepted by Phys. Rev. Lett
12/1997;
-
J. J. Kelly (spokesperson,
E. J. Beise,
H. Breuer,
C C Chang,
N.S. Chant,
F. Duncan,
A. Lung,
P.G. Roos,
A. Sarty (co-spokesperson,
S Barrow, [......],
K. Aniol,
M. Epstein,
D. Margaziotis,
L B Weinstein,
P. Markowitz,
D.S. Dale,
R W Gothe,
M. Benmerrouche,
N. C. Mukhopadhyay,
C. Bennhold
[show abstract]
[hide abstract]
ABSTRACT: We propose to measure cross section and recoil polarization angular distributions for j electroproduction at Q 2 = 0:5 (GeV/c) 2 near the S 11 (1535) resonance. Measurements will be made on both sides of q covering the full range of c.m. angle in steps of 30 ffi , allowing the response functions R LT , R N LT , R 0L LT , R 0S LT , R 0L TT , and R 0S TT to be separated with high precision. These proposed measurements will be complete enough for multipole analysis. The R 0S TT response function is shown to provide a relatively model-independent measurement of jE 0+ j 2 . The unpolarized transverse response function, R T , may receive important contributions from the P 11 (1440) resonance, but those contributions are highly model dependent because neither the electroexcitation form factors nor the jN branching ratio for that resonance are known well. By contrast, P 11 resonances do not contribute in first-order to R 0S TT and the d-wave and nonresonant...
12/1997;
-
R. J. Woo,
D. H. Barkhuff,
W. Bertozzi,
D Dale,
G. Dodson,
K. A. Dow,
M.B. Epstein,
M. Farkhondeh, J.M. Finn,
S Gilad, [......],
P.M. Rutt,
A. J. Sarty,
D. Tieger,
C. Tschalaer,
W. Turchinetz,
P E Ulmer,
C. Vellidis,
S. P. Van Verst,
G. A. Warren,
L. Weinstein
[show abstract]
[hide abstract]
ABSTRACT: The first measurements of the induced proton polarization, P_n, for the 12C (e,e'\vec{p}) reaction are reported. The experiment was performed at quasifree kinematics for energy and momentum transfer (\omega,q) \approx (294 MeV, 756 MeV/c) and sampled a recoil momentum range of 0-250 MeV/c. The induced polarization arises from final-state interactions and for these kinematics is dominated by the real part of the spin-orbit optical potential. The distorted-wave impulse approximation provides good agreement with data for the 1p_{3/2} shell. The data for the continuum suggest that both the 1s_{1/2} shell and underlying l > 1 configurations contribute. Comment: 5 pages LaTeX, 2 postscript figures, accepted by Physical Reveiw Letters
11/1997;
-
J. M. Finn,
R. Madey,
T. Eden,
P. Markowitz,
P. M. Rutt,
K. Beard,
B. D. Anderson,
A. R. Baldwin,
D. Keane,
D. M. Manley, [......],
B. Ni,
M. Spraker,
D. Barkhuff,
R. Lourie,
S. Van Verst,
C. Hyde‐Wright,
W. ‐D. Jiang,
B. Flanders,
P. Pella,
H. Arenhövel
[show abstract]
[hide abstract]
ABSTRACT: Nucleon form factors provide fundamental input for nuclear structure and quark models. Current knowledge of neutron form factors, particularly the electric form factor of the neutron, is insufficient to meet these needs. Developments of high‐duty‐factor accelerators and polarization‐transfer techniques permit new experiments that promise results with small sensitivities to nuclear models. We review the current status of the field, our own work at the MIT/Bates linear accelerator, and future experimental efforts.
AIP Conference Proceedings. 12/1992; 269(1):137-165.
